1. Field of the Invention
This invention relates to a device for controlling blood sugar levels in man, and specifically, to a device for treating diabetic patients.
2. Description of the Prior Art
Diabetes denotes a metabolic disorder caused by a loss in the function of .beta.-cells of the islands of Langerhans in the pancreas of man, which results in their inability to perform a normal secretion of insulin and thus in an insufficient metabolism of blood glucose caused by insulin which eventually leads to an abnormally increased glucose level in the blood. The blood glucose levels of diabetic patients increase at most to about 500 mg%, whereas normal healthy persons have an average blood glucose level of about 80 to 100 mg%.
The one-shot insulin therapy of repeated injections of insulin at intervals of 1 to several days has heretofore been employed to reduce high glucose levels in the blood to normal glucose levels. This method has an effect of reducing the blood glucose level for a certain period of time, but is not sufficient for maintaining the blood glucose level always at an appropriate value. Accordingly, fluctuations in glucose level by external causes such as meals cannot be prevented, and there have been many cases in which diabetic patients suffer from, and die of, renal or cerebral disorders caused by fluctuations in blood glucose levels. An ideal method for treating serious cases of diabetes is to supply insulin depending on the glucose level within the body. In order words, it is desirable to supply insulin in an amount corresponding to the increase in the blood glocuse level, and to stop the insulin supply when the blood glucose level has returned to a normal level.
Methods under investigation in an attempt to establish such an ideal method include a method which is based on linking a glucose sensor to an insulin injector. This method is described, for example, in "Computer Stimulation of the Glucose Regulatory System in Man", Diabetes 19; 1373, (1970). The method involves injecting a required amount of an insulin solution from an injection syringe into the body depending on the glucose level detected by the glucose sensor thereby to maintain the blood glucose level at a normal value. According to this method, however, many accessory devices such as a computer for connecting the injection syringe to the glucose sensor are necessary, and the device as a whole has a large-size. Many problems still have to be solved to put such a device into actual practice.
According to another known method, .beta.-cells removed from the pancreas are cultivated, and are used to perform their inherent function of detecting the blood glucose level in the blood which is present on the other side of a macroporous wall (not a semipermeable membrane) and then releasing insulin, thereby to supply insulin to the blood. Such a method is described, for example, in "A Hybrid Artificial Pancreates" Trans. Amer. Soc. Artif. Int. Organs., 21 8-15 (1975). However, since the tissue culture of the .beta.-cells is difficult, and the cultivated .beta.-cells have a short life, this method is far from practical.